We are interested in measuring the rate of protein synthesis in vivo in man and the rat. N15 is used as the tracer and all N15 measurements are by means of optical emission spectroscopy. Continuous infusion of N15 labelled amino acids for a number of hours results in the attainment of an approximate isotopic steady state in the tissue intracellular amino acid pools. Under such conditions the rate of protein synthesis can be calculated by measuring the amount of N15 in a given tissue protein. In the coming year we propose to continue our investigations on changes in protein synthesis following trauma in the rat, and will attempt to apply our methodology to man. BIBLIOGRAPHIC REFERENCES: Stein, T. P., Leskiw, M. J., Liquori, E. M., Brooks, H. B., Wallace, H. W. and Blakemore, W. S. The use of optical emission spectroscopy for human N15 tracer studies. Anal. Biochem., 66: 481-488, 1975.